The present invention relates to a pressure-sensor-integrated glow plug where a pressure sensor for detecting a cylinder inner pressure is integrally mounted on a sheath type glow plug used for assisting starting of a diesel engine, and a method of manufacturing the pressure-sensor-integrated glow plug.
Conventionally, in a diesel engine which is a self-ignition-type internal combustion engine, a ceramic heater type glow plug where a heat generating part is formed of a ceramic material is disposed in the inside of a combustion chamber. Recently, a pressure-sensor-integrated glow plug where a pressure sensor for detecting a cylinder inner pressure and a glow plug are integrally formed with each other has been put into a practical use.
For example, a ceramic heater type glow plug includes: a housing inserted into the inside of a combustion chamber; a ceramic heater element having a distal end thereof projecting from the housing and held on the housing; and a pressure sensor arranged between the ceramic heater element and the housing. The pressure sensor-integrated glow plug is configured such that the ceramic heater element is held on the housing by means of a flexible member such as a diaphragm, the ceramic heater element is displaced in an axial direction in the housing due to a cylinder inner pressure, and the pressure sensor can detect the cylinder inner pressure based on this displacement.
The ceramic heater element includes: a ceramic heater; a metal-made outer sleeve holding the ceramic heater on one end side thereof and having the other end side thereof inserted into and fixed to an inner hole of the housing; and a conductor portion electrically connected to an electrode of the ceramic heater and led out to the other end side of the metal-made outer sleeve. In the pressure-sensor-integrated glow plug provided with such a ceramic heater element, a gap formed between the ceramic heater element and the housing is sealed in an airtight manner with respect to the combustion chamber by the flexible member, and the airtightness in the ceramic heater element is ensured by bonding the metal-made outer sleeve and the ceramic heater to each other. Due to such a constitution, for example, it is possible to prevent the occurrence of a drawback such as breaking of an electronic printed circuit board mounted on a rear end side of the housing due to soot in an exhaust gas or the like.
With only the bonding portion between the ceramic heater and the metal-made outer sleeve, the bonding portion is deteriorated due to a thermal load in the combustion chamber so that airtightness is reduced. In view of the above, there has been disclosed a glow plug where a metal material having a low thermal expansion coefficient is used for forming a seal element, and the seal element is bonded to a metal-made outer sleeve so as to ensure airtightness (see JP-T-2010-521645, for example).